*23. A coin having a probability of coming up heads is successively flipped until the rth...

*23. A coin having a probability ñ of coming up heads is successively flipped until the rth head appears. Argue that X, the number of flips required, will be ç, ç > r, with probability xx\x2\ ···xr\ ÑÚÑ×22·-Ñ×/ when xx + x2 + · · · + xr = ç

ç > r This is known as the negative binomial distribution.